1. Field of the Invention
The present invention relates to an improved multi-point distance measuring device capable of obtaining information on distance measurement in a plurality of areas.
2. Description of the Related Art
A passive distance measurement apparatus employs a method whereby reflected light from an object is divided in two so as to determine the distance from the object on the basis of the amount of a relative shift between the two optical images that are respectively formed thereby. This type of conventional distance measuring device has found extensive use in cameras and the like.
For instance, Japanese Examined Patent Publication No. 6-100717 discloses a construction in which distance measurement is performed at a plurality of points in carrying out passive distance measurement. If the measurement result indicates that an object has a low illuminance level and low contrast, then auxiliary light is irradiated onto the object and the distance measurement is performed only in a particular area.
It is generally accepted that the passive distance measurement method is not good at performing distance measurement on an object with a low illuminance and low contrast. In order to obtain reliable distance measurement information from an object with a low illuminance and low contrast, auxiliary light is irradiated onto the object to acquire the distance information at least on a particular point.
In addition to a through-the-lens (TTL) type distance measuring device, there is an external measurement type distance measuring device. U.S. Pat. No. 5,051,767 discloses an external measurement type distance measuring device that changes the operating range of a line sensor on the basis of the focal length of a shooting optical system. For instance, in an external measurement type device in which the focal length of the shooting optical system can be changed, while the distance measurement area cannot be changed, the distance measurement area moves toward the outside of a shooting image view angle range as the focal length increases. Hence, when the focal length exceeds a certain value, the distance measurement area will be outside a shooting image view angle, which is the image view angle range that permits shooting.
For this reason, a device has been provided that carries out a control operation that prevents distance measurement from being performed outside a shooting image view angle range.
In one aspect, the present invention relates to a distance measuring device, or a focus detector, having sensors for a plurality of areas and respective processing circuits for the sensors, wherein power is supplied only to a sensor and a processing circuit associated with a predetermined area.
In another aspect, the present invention relates to a distance measuring device, or a focus detector, having sensors for a plurality of areas and processing circuits for the sensors, wherein the sensors and the processing circuits to which power is to be simultaneously supplied are selected according to the condition of a power source that supplies power to the sensors and the processing circuits.
In still another aspect, the present invention relates to a distance measuring device, or a focus detector, having sensors for a plurality of areas and processing circuits for the sensors, wherein the sensors and the processing circuits to which power is to be supplied are selected according to the focal length of a shooting optical system.
In a further aspect, the present invention relates to a distance measuring device, or a focus detector, having sensors for a plurality of areas and processing circuits for the sensors, wherein the sensors and the processing circuits to which power is to be supplied are selected according to the area to which auxiliary light is projected.
In yet another aspect, the present invention relates to a camera having a distance measuring device, or focus detector, as described above.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.